The Centers for Disease Control and Prevention (CDC), estimates that one in every six Americans gets sick from foodborne illness each year, results in 128,000 hospitalizations and 3,000 deaths. Foodborne pathogens deteriorate the quality of food, causing increased food wastage. Recent foodborne microbial outbreaks are driving a search for innovative ways to inhibit microbial growth in foods while maintaining quality, freshness, and safety and extend the shelf-life of fresh produces. The Federal government advises and encourages healthy eating habits, which includes consumption of a variety of fresh fruits and vegetables1,2. As a result, the per capita consumption of eating fresh produce has increased to $12 billion annual sales in the past few years3,4 and the fresh-cut food industry sector becomes the fastest growing segment of food industries. As the fresh-cut produce market continues to grow, such producers face the challenge of an increase in microbial safety for longer shelf life. From 1996 to 2006, 22 foodborne illness outbreaks were associated with the consumption of fresh produce. Of these outbreaks, according to Food and Drug Administration (FDA), 18 outbreaks were implicated by fresh-cut produce. Foodborne illness outbreaks also impact the fresh produce trade leading to economic losses4. Food related epidemic can be prevented by means of improved surveillance and detection of contaminations, enhanced epidemiological investigation, safe packaging, and effective methods to identify pathogens5-10.
The packaging of fresh fruits and vegetables is one of the most important steps in the long supply chain from the producer to the consumer. Protecting the fresh produce by packing them in antimicrobial (AM) films can extend their shelf life of food11-14. They also effectively control the foodborne pathogens and food-spoiling microorganisms. These packages are typically manufactured by incorporating antimicrobial agents, immobilized or coated on the surface of the packaging material. Even though the AM packaging films and number of antimicrobial agents have been studied for many years, commercial successes of these packaging materials are very limited due to many constraints in large scale production15. Selection of packaging systems and the antimicrobial agents are very critical as they would influence the inherent physicochemical properties of food. Now there is also an increasing demand for green labeling and environmental safety, leading to an increasing number of R & D efforts in the field of biodegradable food packaging materials. Instead of using polymer materials derived from petroleum products, biopolymers derived from renewable sources (starch, cellulose, protein etc.) are more favorable in developing an eco-friendly packaging system for food. When the antimicrobial agents are combined with biodegradable packaging materials, it features the merits of the packaging system in terms of food safety, shelf-life, and environmental friendliness.
Cellulose is one of the most abundantly available biopolymers and it is a linear carbohydrate polymer chain that contains D-glucopyranose units joined together by β-1,4-glycosidic linkages. The cellulose pulp derived from plants and trees are either mechanically or chemically fibrillated into nanocellulose fibrils (CNF) having 5-20 nm diameter. These nanocellulose fibrils highly influence the properties and functionality of the final products16-19. George et al made food packaging membranes using nanocellulose derived from bacterial cellulose and demonstrated its relevance as a packaging material for the food industry20. The prepared membrane possessed minimal oxygen permeability, good mechanical stability, and controlled water permeability, which are critical for food packaging materials to maintain the quality of packed food. Reinforcing nanocellulose with other long chain polymers such as chitosan to develop biodegradable nanocomposite food packaging materials can further improve the quality of the packaging material as well as long storage life21.
Antimicrobial films with controlled release of antimicrobial agents are more advantageous than dipping or spraying the food with antimicrobial agents containing edible polymers22-24. In these types of coatings, the antimicrobial activity is lost due to its inactivation by the food components leading to concentrations dropping below active levels25. There are several antimicrobial agents available to incorporate into packaging films. However, each one has its own disadvantages apart from their noted advantages. Sodium nitrite salt has been used for centuries in meat curing. Nitric oxide (NO) released from this salt terminates free radicals present in lipid oxidation and provide the typical property for the cured meat26. There are many NO-donating compounds such as nitrates and nitrites that have been used for several years in curing and preserving meats, fish, and certain cheeses27, 28. Nitric oxide inhibits the growth of wide varieties of bacteria (both gram positive and gram negative), viruses, fungi, and yeast29-31. The biggest advantage of NO as an antimicrobial agent is its antimicrobial activity against antibiotic-resistant strains32-34. However, incorporating NO donor compounds such as S-nitrosothiols in the packaging materials for food has not been yet studied. In this study, we investigated the effects of incorporating the NO donor, S-Nitroso-N-acetylpenicillamine (SNAP) into biodegradable nanocellulose-chitosan composite membranes for increased antimicrobial activity for potential food packaging application.